This invention relates generally to hydraulic systems for engines, and more particularly to a device and method for pre-pressurizing fluid in a common rail for an engine hydraulic system.
An example of a typical hydraulic system for an engine might be a set of hydraulically actuated fuel injectors that utilize engine lubricating oil as their actuation fluid medium. It has long been known that engine lubricating oil expands and contracts as much as 15% or more in volume over the expected temperature range that the engine will encounter. For instance, an engine can fall to relatively low temperatures, possibly below 0xc2x0 F., when not running in a low temperature environment and can experience substantially higher temperatures when running for a prolonged period in a relatively warm ambient environment. When an engine is running and for some duration after being shut down, the hydraulic systems for the engine will be substantially completely full of lubricating oil. However, as the engine cools, the lubricating oil in the hydraulic system tends to contract and create fluid voids in such areas as the common rail and/or pump priming reservoir of the hydraulic system. While the formation of these fluid voids is expected and not harmful to the engine or hydraulic system, some undesirable results can occur. For instance, when the engine is restarted after a substantial cooling period, a sometimes annoying excessive cranking of the engine is required in order to bring the hydraulic system back up to full pressure to start the engine anew. While this excessive cranking is not indicative of an actual problem, it can be misperceived as a problem by the engine user.
The prior art has addressed this problem by using priming reservoirs such as that shown in U.S. Pat. No. 5,245,970 issued to Iwaszkiewicz et al. on Sep. 21, 1993. The priming reservoir is positioned above the inlet of the high pressure pump and above the common rail passage so that the fluid in the priming reservoir will flow by gravity and/or suction to keep the common rail passage and high pressure pump inlet passage filled with fluid when the high pressure pump is not operating. While these priming reservoirs can reduce crank time, there is room for improvement. For instance, priming reservoirs may not be suitable in vehicles or work machines where there is insufficient space for the priming reservoir above the pump mounting location or the common rail. Further, during startup the high pressure pump must pressurize the entire system before the engine can start.
The present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the invention, a method of pressurizing a hydraulic system for an engine includes a first step of reducing a fluid volume of the hydraulic system until fluid pressure reaches a predetermined pressure. After the engine is started, pressure in the hydraulic system is sustained at least in part by further reducing the fluid volume of the hydraulic system.
In another aspect, a method of reducing crank time during engine startup for an engine with a hydraulic system includes the step of pressurizing fluid in the hydraulic system at least in part by reducing a fluid volume of the hydraulic system.
In still another aspect, a hydraulic system for an engine includes a common rail with an inlet and at least one outlet. The inlet of the common rail is fluidly connected to the outlet of a pump. The outlet of the common rail is fluidly connected to the inlet of at least one hydraulic device. A volume reducer includes a member that moves into and out of the common rail.